Cryptosporidium parvum is recognized as an important cause of diarrhea worldwide and can cause life-threatening disease in immunocompromised patients. The organism is detected in 65-97% of the surface-water supply in the United States and is resistant to most disinfectants used for treatment of drinking water. Currently, there is no drug therapy or vaccine that is effective against C parvum. This research will be directed towards the development of an oral vaccine against C parvum. Antibodies in the serum of humans and animals infected with C parvum react with several antigens, one of which is a 15 kDa protein (CP15) located on the surface of the organism. This protein is a good candidate for use as a molecular vaccine because previous studies have shown that a monoclonal antibody to CP15 confers passive immunity to mice. This research will determine if orally administered recombinant CP15 will elicit humoral and/or mucosal immune responses. In addition, some immunizations will include a form of Escherichia coli LT toxin known to function as an oral adjuvant and its effect on the immune response will be determined. Finally, transgenic potato plants will be developed as a low cost approach to produce recombinant CP15. PROPOSED COMMERCIAL APPLICATION: Development of transgenic plants expressing Cryptosporidium parvum antigens for use as an oral vaccine against crptosporidiosis.